This invention relates to a cryogenic envelope for a transmission line. In this respect, a preferred embodiment of the invention will be described in connection with a laminar insulated cryogenic envelope for a flexible superconducting power transmission line.
In order to be commercially attractive, superconductive power transmission lines must have low thermal losses and high reliability. Consequently, it is an object of this invention to provide a transmission line having an insulated cryogenic envelope that is both reliable and results in a low heat-leak.
It is not uncommon for Dewar type cryogenic vessels to direct refrigeration through tubes to shields located between layers of laminar insulation within the container's vacuum space. Refrigeration tubes present a problem, however, in that it is difficult to prevent heat from leaking to them from the members which separate and provide a vacuum seal between the transmission line and the surrounding vacuum jacket. The illustrated transmission line, however, includes "reentry" structure for reducing the heat-leak that is permitted to enter the line's interior.
In the above respect, the transmission of refrigeration from refrigeration tubes to refrigeration shields presents a problem in that the tubes tend to expand or contract at a rate that is different from the shields. Hence, the embodiment about to be described includes a type of shield that is adapted to maintain good thermal contact with the refrigeration tube, but nevertheless is free to expand or contract at a different rate.